Large-scale mining operations in Alaska’s Bristol Bay will harm habitat for wild salmon, the Environmental Protection Agency concluded in a draft assessment Friday, but agency officials said they had not decided whether they would move to block a proposal for a major gold and copper mine there.

The Nushagak and Kvichak watersheds produce nearly half the world’s sockeye salmon. Tribal leaders, environmentalists and salmon-fishing operators have lobbied the EPA to invoke the Clean Water Act, which includes provisions protecting fishery areas, to block the mining project proposed by Northern Dynasty Minerals, a Canadian company.

The company announced this week it would spend roughly $107 million to prepare its Pebble Mine project for permitting by the end of the year. The firm will produce a detailed description of the project, which could produce more than 80 billion pounds of copper, 107 million ounces of gold and 5.6 billion pounds of molybdenum.

Northern Dynasty Minerals and its subsidiary, Pebble Limited Partnership, estimate the mine could also produce 2,000 jobs during construction and 1,000 jobs when it is operating.

In a call with reporters Friday, the EPA’s Region 10 administrator, Dennis McLerran, said large-scale mining is likely “to have adverse impact on the productivity and sustainability of the salmon fishery” in Bristol Bay, primarily through destruction of habitat.

Large-scale mining operations in Alaska’s Bristol Bay will harm habitat for wild salmon, the Environmental Protection Agency concluded in a draft assessment Friday, but agency officials said they had not decided whether they would move to block a proposal for a major gold and copper mine there. (Isaac Babcock/AP)

McLerran, who described the draft as “a scientific document” and not “a regulatory decision,” emphasized that it was an analysis of the potential impact of a hypothetical scenario rather than of a specific project.

“The assessment is not about a single mine,” he said, noting that in addition to Pebble, “at least seven mine proposals are in advanced stages of exploration and development.”

The study estimated that a large-scale mine “would likely result in the direct loss of [54 to 87.9 miles] of streams and [3.9 to 6.7 square miles] of wetlands.” It added that water withdrawals for mine operations “would significantly diminish habitat quality in an additional [1.2 to 6.2 miles] of streams.”

It also stated that while it was highly unlikely that dams containing mine tailings would break, other “potential accidents” include acid, metal and other contaminants being released from the mine site, waste-rock piles or tailings storage, or spilled copper concentrate.

“Though precise estimates of the probabilities of failure occurrence cannot be made, evidence from the long-term operation of similar large mines suggests that, over the life span of a large mine, at least one or more accidents or failures could occur, potentially resulting in immediate, severe impacts on salmon and detrimental, long-term impacts on salmon habitat,” the analysis said.

In a telephone interview Friday, John Shively, chief executive of the Pebble Limited Partnership, questioned the assessment’s integrity given that it was conducted in just one year.

“We’ve been studying a small part of these two watersheds for eight years,” he said, adding that the company had spent $120 million on scientific studies so far. “We don’t understand how [the EPA’s draft assessment] can possibly be adequate and meet their standards.”

Shively added that while President Obama has pledged to streamline the federal permitting process, the EPA has been complicating the permitting process before it has begun.

“The issue is how are we going to design a mine that protects fish,” he said. “You figure that out in the permitting process. We understand the fish need to be protected. We want an opportunity to prove it.”

However, many fishing operators and Bristol Bay residents said any mining operation could jeopardize the area’s average annual run of 37.5 million sockeye salmon. The EPA estimated that Bristol Bay’s wild salmon fishery and other ecological resources generate $480 million in annual revenue and provide at least 14,000 full-time and part-time jobs.

“What I read here is pretty definitive. There will be loss of habitat and impacts on the fishery in any large-scale mining scenario in the area,” said Lindsay Bloom, who fishes for sockeye salmon as captain of the ship Rainy Dawn. “It’s really nice to see someone finally taking this seriously.”

Sharon Leighow, spokeswoman for Alaska Gov. Sean Parnell (R), said the governor “will work to ensure any new development fully protects the resource values of the area” but believes “the EPA has clearly overreached with this unprecedented process. Without a specific proposal, the EPA cannot evaluate the potential impacts or risks from the project.”

Elizabeth Dubovsky, salmon outreach director for Trout Unlimited’s Alaska program, said she was confident that the analysis would lead the Obama administration to block mining operations in Bristol Bay.

“This is not about being anti-mining. This is about recognizing that some places are not appropriate for these sorts of industrial activities,” Dubovsky said. “For the first time, we now have the information in hand for Obama to take action on that.”

Staff researcher Eddy J. Palanzo contributed to this report.

Juliet Eilperin is The Washington Post's White House bureau chief, covering domestic and foreign policy as well as the culture of 1600 Pennsylvania Avenue. She is the author of two books—one on sharks, and another on Congress, not to be confused with each other—and has worked for the Post since 1998.

Comments our editors find particularly useful or relevant are displayed in Top Comments, as are comments by users with these badges: . Replies to those posts appear here, as well as posts by staff writers.

To pause and restart automatic updates, click "Live" or "Paused". If paused, you'll be notified of the number of additional comments that have come in.

Comments our editors find particularly useful or relevant are displayed in Top Comments, as are comments by users with these badges: . Replies to those posts appear here, as well as posts by staff writers.